<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Tree Menu Example</title>
<style>
  ul {
    list-style-type: none;
    padding: 0;
  }
  ul ul {
    margin-left: 20px;
  }
  li {
    margin: 5px 0;
  }
</style>
</head>
<body>

<ul>
  <li>Menu Item 1
    <ul>
      <li>Submenu Item 1.1
        <ul>
          <li>Sub-Submenu Item 1.1.1</li>
          <li>Sub-Submenu Item 1.1.2</li>
        </ul>
      </li>
      <li>Submenu Item 1.2</li>
    </ul>
  </li>
  <li>Menu Item 2
    <ul>
      <li>Submenu Item 2.1</li>
      <li>Submenu Item 2.2
        <ul>
          <li>Sub-Submenu Item 2.2.1</li>
          <li>Sub-Submenu Item 2.2.2</li>
        </ul>
      </li>
    </ul>
  </li>
  <li>Menu Item 3</li>
</ul>

</body>
</html>